Pick-up tube having a mesh electrode connected to the base by deflecting field neutralizing leads



Nov. 15, 1966 H. G. LUBSZYNSKI 3,286,121

PICK-UP TUBE HAVING A MESH ELECTRODE CONNECTED TO THE BASE BY DEFLECTING FIELD NEUTRALIZING LEADS Filed Jan. 10, 1963 United States Patent M 3,286,121 PICK-UP TUBE HAVING A MESH ELECTRODE CONNECTED TO THE BASE BY DEFLECTING FIELD NEUTRALIZING LEADS Hans Gerhard Lubszynski, Waltham St. Lawrence, England, assignor to Electrical & Musical Industries Limited, Hayes, Middlesex, England, a company of Great Britain Filed Jan. 10, 1963, Ser. No. 250,535 Claims priority, application Great Britain, Jan. 15, 1962, 1,421/ 62 3 Claims. (Cl. 315-8) This invention relates to pickup devices, such for example as vidicons, and to circuit arrangements embodying such devices.

Photoconductive devices such as vidicons are employed for converting light images into electrical signals, for example for television, and such devices comprise a photoconductive target on to which the light image is projected, and an electron gun whereby an electron beam may be generated for scanning the target, so as to produce the electrical signals. Deflecting coils are usually applied to the envelope of the device, so as to produce a deflecting field for causing the beam to scan the target and it is also usual to provide within the envelope a cylindrical wall anode which encloses the region in which the deflecting field is set up.

It has, moreover, been proposed to provide another electrode in the form of a mesh extended before the target and between the wall anode and the target, this mesh and the wall anode having separate connections whereby they may be maintained at different potentials. However, it is inconvenient to make separate .connection to this mesh electrode by means of a 'lead passing through the envelope at the target end of the device, so that connection is made in practice by means of a lead which extends within the envelope from the mesh electrode to the vicinity of the gun, where this lead is connected to one of the wires in the pinch or to one of the gun electrodes. It has been found, however, that with this construction a spurious signal of relatively large amplitude tends to appear at the signal output of the device, this spurious signal being apparently picked up from the line scanning coils, especially during flyback, by the lead to the mesh electrode, and transferred to the signal plate by capacitive coupling.

A similar disadvantage may arise in other image pickup devices having an electrode coupled capacitively with the signal output electrode and liable to receive spurious signals picked up from the deflecting coils. The object of the present invention is to reduce this disadvantage.

According to the present invention there is provided an electron discharge device having a target, an electrode so disposed relative to said target that capacitive coupling exists between said electrode and said target, and wherein for the purpose of applying potential to said electrode a plurality of leads are provided within the envelope extending to the electrode through a region in which a deflecting field exists during operation of the device, said leads being so disposed that during operation, spurious signals picked up by the different leads from the deflecting field are substantially mutually cancelling.

In order that the present invention may be clearly understood and readily carried into effect it will now be more 'fully described with reference to the accompanying drawing in which:

FIGURE 1 illustrates one example of a circuit arrangement embodying a vidicon pick-up tube in accordance with the present invention, and

FIGURE 2 illustrates a modification of FIGURE 1.

Referring to FIGURE 1, the pick-up tube comprises a tubular envelope 1 having an end wall 2, on the inner surface of which is deposited first a conductive signal 3,286,121 Patented Nov. 15, 1966 plate 3 and second a photoconductive target 4. Arranged within the envelope 1 is a mesh electrode 5 which is parallel to the target 4, a wall anode 6, and an electron gun generally denoted by the reference 7. The gun comprises an electron emitting cathode 8, a cathode shield or so called modulator electrode 9 and a double apertured limiter electrode 10, sometimes called an anode, these electrodes being connected to current carrying pins 11 sealed into the base or pinch 12 of the envelope 1. 1 The mesh electrode 5 is isolated from the wall anode 6, the mesh electrode being mounted in any convenient manner in the envelope, being, for example, secured to a metal ring 13. The gun electrodes 8, 9 and 10 and the wall anode 6 are assembled as a unit structure and held separated from each other 'by means of insulating support rods which are not shown but which are in themselves well known in this art. This structure is also provided with two conductive leads 14 and 15 which (in this example) are connected to the limiter electrode 10 and at their ends are provided with spring members 16 and 17 which make electrical contact with the ring 13 and thereby with the mesh electrode 5. The leads 14 and 15 are preferably arranged within closely fitting glass or other insulating tubes such as ceramic tubes so as to insulate the leads from the other electrodes, and these tubes may in turn be supported from the wall anode 6 by means of small metal straps which surround the glass tube and which are welded at their ends to the wall anode 6. The two leads are, as indicated, arranged to be diametrically opposite each other, with reference to the axis of the tube.

For operating the tube, appropriate potentials, such as those indicated in the drawing, are applied to the various electrodes. Deflecting coils are, moreover, fitted on the exterior of the envelope, such coils being denoted generally 'by the reference 18 in the drawing. A focussing solenoid 19 is moreover, fitted so as to enclose the tube and the scanning coils. When the tube is operated it is found that, by reason of the balanced arrangement of the leads 14 and 15, substantial spurious signals picked up from the line scanning coils by the leads 14 and 15 are equal and of opposite sign and so do not appear on the mesh 5 and cannot therefore be transferred to the signal output of the tube obtained across the resistor 20 connected to the signal plate.

The leads for making connection to the mesh electrode 5 need not be connected as shown to one of the gun electrodes but may be connected to an individual pin in the base 12 of the envelope, as shown in FIGURE 2.

As aforesaid, the invention may be applied to pick-up devices other than vidicons in which there is an electrode, so close to the target that capacitive coupling exists between that electrode and the target, and which is liable to receive spurious signals picked up from the deflecting coils.

What I claim is:

1. A pickup device including an evacuated envelope and within said envelope, a target, an electron gun, a mesh electrode disposed between said target and said gun and placed sufficiently close to said target to have substantial capacitive coupling thereto, and a wall anode, the device also having a plurality of contact members attached to said envelope adjacent to said electron gun, means for setting up during operation of the device a deflecting field for a beam of electrons emitted by said gun to cause said beam to scan said target, and means connecting said mesh electrode to at least one of said contact members, said connecting means including in the region of said deflecting field at least one pair of leads running along the device and diametrically opposite in relation to the axis thereof; so that spurious signal picked up by one lead of the pair from the deflecting field is substantially cancelled connection to electrodes within said envelope, and con- 10 necting means from said mesh electrode to at least one of said contact members, said connecting means including alongside said wall anode at least one pair of leads along the device and diametrically opposite with respect to its axis.

3. A tube according to claim 2 wherein said target is photo conductive.

References Cited by the Examiner UNITED STATES PATENTS 4/1960 Lubszynski et al 313-65 10/1964 Poole et a1 3158 JAMES w. LAWRENCE, Primary Examiner.

R. SEGAL, Assistant Examiner. 

2. A PICKUP DEVICE COMPRISING AN EVACUATED ENVELOPE WITHIN WHICH ARE DISPOSED A TARGET, AN ELECTRON GUN, A MESH ELECTRODE CLOSE AND SUBSTANTIALLY PARALLEL TO SAID TARGET AND A WALL ANODE, BOTH SAID MESH ELECTRODE AND SAID WALL ANODE BEING PLACED BETWEEN SAID TARGET AND SAID GUN, THE DEVICE ALSO HAVING A PLURALITY OF CONTACT MEMBERS ATTACHED TO SAID ENVELOPE ADJACENT TO SAID GUN TO ENABLE CONNECTION TO ELECTRODES WITHIN SAID ENVELOPE, AND CONNECTING MEANS FROM SAID MESH ELECTRODE TO AT LEAST ONE OF SAID CONTACT MEMBERS, SAID CONNECTING MEANS INCLUDING ALONGSIDE SAID WALL ANODE AT LEAST ONE PAIR OF LEADS ALONG THE DEVICE AND DIAMETRICALLY OPPOSITE WITH RESPECT TO ITS AXIS. 